Manufacture of detonating fuse cord

ABSTRACT

DETONATING FUSE CORD HAVING ALONG ITS LENGTH ALTERNATING SECTIONS OF GREATER AND LESSER EXPLOSIVE ENERGY IS MANUFACTURED BY FORMING DRY PARTICULATE EXPLOSIVE INTO A CORE ABOUT A CENTRE THREADLINE IN SUCH A MANNER THAT THE CORE IS MADE UP OF CONNECTED SECTIONS OF GREATER AND LESSER EXPLOSIVE MASS. THE CORE IS THEREAFTER ENVELOPED WITH A PROTECTIVE COVERING.

NOV. 23, 1971 WELSH ETAL 3,621,558

MANUFACTURE OF DETONATING FUSE CORD Filed Jan. 19, 1970 '2 Sheets-Shoat1 .1: an-12 m INVEN'IURS Peter Edgar PHILLIPS David Martin WELSH Nov.23, 1971 D. M. WELSH ETAL 3,621,558

MANUFACTURE OF DETONAT ING FUSE CORD 2 Shoots-Shoat 2 Filed Jan. 19,1970 v INVEN'I'ORS Peter Edgar PHILLIPS David Martin WELSH AGENT UnitedStates Patent 3,621,558 MANUFACTURE OF DETONATING FUSE CORD David MartinWelsh and Peter Edgar Phillips, Brownsburg, Quebec, Canada, assignors toCanadian Safety Fuse Company Limited, Montreal, Quebec, Canada FiledJan. 19, 1970, Ser. No. 3,860 Claims priority, application Canada, May6, 1969,

Int. Cl. B22f US. Cl. 29420 2 Claims ABSTRACT OF THE DISCLOSUREDetonating fuse cord having along its length alternating sections ofgreater and lesser explosive energy is manufactured by forming dryparticulate explosive into a core about a centre threadline in such amanner that the core is made up of connected sections of greater andlesser explosive mass. The core is thereafter enveloped with aprotective covering.

This invention relates to detonating cord and in particular, to themanufacture of a detonating cord having an explosive core of alternatingcore sections of controlled variations. Such a detonating cord hasparticular use in, for example, metal expansion applications.

As is known in the explosives art, detonating cords are normallyproduced in long or continuous lengths and comprise essentially auniform core of explosive encased in a protective wrapping or sheath.Originally, the protective sheath consisted of a soft metal such as leadbut these lead sheathed cords have now generally been superseded bythose having sheaths consisting of water resistant tape or textilewrappings, synthetic plastics and the like. The amount of explosive perfoot of length in the core may vary from a small quantity of from 0.1 toabout grains, as in low energy detonating cord (LEDC), to as much as 50grains or more. Typical explosives employed as core material are, forexample, pentaerythritoltetranitrate (PETN),cyclotrimethylenetrinitramine (RDX), nitromannite, lead azide,trinitrotoluene (TNT), cyclotetramethylenetetranitramine (HMX), leadstyphnate or tetryl and mixtures of these.

In the explosives industry detonating cords are manufactured by one orother of the dry or wet processes. In the dry process relatively coarse,particulate, dry explosive which comprises the core material of the cordis encased in a continuous column by means of a wrap of tape-likematerial and thereafter encircled by means of textile yarns or the like.The cord may thereafter be coated with a waterproofing surface layer ofpitch, thermoplastic or the like. The dry process is normally employedin the manufacture of detonating cords having a core load of 25 grainsor more of explosive per foot of length.

In the wet process, the core is formed from a thickened aqueous slurryof particulate explosive which is wrapped and covered in much the samemanner as that employed in the dry process. Generally the wet process isemployed in the manufacture of detonating cord having a core load of 4grains or more of explosive per foot of length.

It has heretofore been the object and concern of the explosives industryto manufacture detonating cords having an absolute minimum of core loadvariation throughout the cord length in order to ensure constantdetonation characteristics along the cord, in particular, uniformlateral energy output. It has now been found that in certainapplications such as metal expansion, it is desirable to provide adetonating cord having an alternating or pulsating lateral energy outputwith a substantially constant linear velocity of detonation.

"Ice

Accordingly, it is an object of the present invention to provide amethod of manufacture of detonating cord wherein the cord contains acontinuous explosive core load, which core load comprises alternatingsections of greater and lesser explosive energy.

Other objects of the invention will become obvious from a considerationof the following disclosure and claims.

The novel method of manufacture of the invention comprises the steps ofdirecting a stream of dry particulate explosive through an orifice andenveloping the stream with a wrapping means in such a manner thatregular, alternating sections of the resulting explosives column havedifferent energy outputs.

The method of the invention and the product thereof may be more fullyunderstood by reference to the accompanying drawings wherein:

FIG. 1 is a sectional view of one embodiment of a finished detonatingcord made by the method of this invention.

FIG. 2 is a sectional view of a second embodiment of a finisheddetonating cord made by the method of this invention;

FIG. 3 is an elevational diagrammatic view of a portion of an apparatussuitable for use in the method of the invention; and

FIG. 4 is an elevational diagrammatic view of an alternative arrangementof an apparatus suitable for use in the method of the invention.

Referring in detail to FIG. 1, there is shown a detonating cord 1 havingan inner threadline 2. Threadline 2, made of twisted or braided cotton,linen or the like, comprises alternating thick and thin sections shownas 3 and 4 respectively. Explosive charge 5 surrounds threadline 2 andassumes the shape of interconnected heavy and light explosive sections 6and 7 respectively. Explosive charge 5 is enveloped by a wrap of papertape or the like 8 and an overlay of filament wraps 9 and the whole hasan outer covering 10 of, for example, a flexible thermoplastic material.

Referring to FIG. 3, there is shown an apparatus which may be employedto manufacture the detonating cord of FIG. 1 and which comprises acenter thread, gravity feed fuse making apparatus well known in the art.In operation, a medium fine to very fine granular explosive such asPETN, from a storage hopper is continuously delivered by feed means 11into a tapered funnel-shaped hopper 12. A cord or thread 13 havingalternating thick and thin sections 3 and 4 is passed from a source (notshown) continuously downward through the neck 14 of hopper 12. Thepassage of thread 13 through hopper 12 and the granular explosivecontained therein, carries the explosive through neck 14 in alternatingquantities in cooperation with the thick and thin sections of thread 13.As the thread and explosive emerges from neck 14 in columnar form ofconstant diameter it is enveloped by a tape 15 of, for example, paper orplastic and thereafter overwrapped by textile threads 16 and 17 locatedon textile spinning head 18. The semi-finished cord is then passed overpulley 19 and forwarded to an outer protective sheath applicationstation (not shown) after which it may be wound on a take-up spool forstorage or shipment.

Referring to FIG. 2, there is shown a detonating cord 20 having an innerexplosive core 21 comprised of a filament wrapped column of detonatingcord having a core load of, for example, 25 grains of PETN per linearfoot. Additional quantities of PETN explosive 22 surround core 21 inspaced-apart sections along the length of core 21. Core 21 and addedexplosive sections 22 are enveloped by a tape of paper or plastic 23 andan overlay of filament yarn 24 and the whole has an outer covering 25of, for example, a flexible thermoplastic material.

Referring to FIG. 4, there is shown an apparatus which may be employedto manufacture the detonating cord of FIG. 2. The apparatus shown inFIG. 4 comprises, in general, a well known type of center thread,gravity feed, fuse making device but which has been modified forpurposes of the method of the invention. In operation, an unsheathed,filament-wrapped detonating cord 30 comprising, for example, 25 grainsof PETN per linear foot, is continuously fed from a source (not shown)downward through the neck 31 of funnel-shaped hopper 3 2. The opening inneck 31 is slightly larger than the space occupied by cord 30. A mediumfine to very fine granular explosive 33 such as PETN is delivered inalternating, measured quantities by feed means 34 into hopper 32. Cord30 together with the delivered portion or slug of PETN 33 pass throughthe neck 31 where they are immediately Wrapped by tape 35 and thereafteroverwrapped by textile threads 36 and 37 located on textile spinninghead 38. The semi-finished cord is then passed over pulley 39 andforwarded to an outer protective sheath application station (not shown)after which it may be wrapped on a take-up spool for storage orshipment.

The core sections of greater and lesser quantity of explosive which maytake the form of thick and thin sections of finished cord, as shown inFIG. 2, or which may take the form of a cord of constant externalthickness about a centre threadline, as shown in FIG. 1, may be made inany desired combinations by varying the steps of the method. In usingthe apparatus of FIG. 3, for example, the centre thread or cord 13 maybe constructed in a range of thicknesses or length in its sections 3 and4 and, at the same time the size of neck 14 may be altered to allow moreor less of the explosive to emerge from hopper 12. In using theapparatus of FIG. 4, for example, the core load of the center fuse-cord30 may be varied as may be the quantity of explosive 33 deposited intohopper 32.

It will be obvious from the foregoing description that detonating corecomprising alternating connected sections of greater and lesserexplosive energy may also be produced through the use of, for example,explosives having different energy values or strengths. That is to say,the continuous column of light core 21 in FIG. 2 may comprise, forexample, PETN while the added explosive in the heavy section 22 maycomprise, for example, TNT.

We claim:

1. A method of continuously producing detonating fuse cord having alongits length alternating sections of different potential energy outputs,comprising the steps of:

(a) providing high explosive material in dry particulate form,

(1)) depositing the high explosive material about axially spaced apartsections of an unsheathed detonating cord of constant diameter and (c)enveloping the high explosive material with a covering as it isdeposited on the cord.

2. A method as claimed in claim 1 wherein the dry particulate highexplosive is selected from the group consisting ofpentaerythritoltetranitrate, cyclotrimethylenetrinitramine,nitromannite, lead azide, trinitrotoluene,cyclotetramethylenetetranitramine, lead styphnate, tetryl and mixturesof these.

References Cited UNITED STATES PATENTS 1,275,001 8/1918 Dormer 102-271,674,773 I 6/1928 Fritzsche 102-27 3,318,242 5/1967 Grifiith 102--27 X3,367,266 2/1968 Griffith 10227 3,382,802 5/1968 Prior et a1 l02273,435,764 4/1969 Kelly et al 10227 JOHN F. CAMPBELL, Primary Examiner V.A. DIPALMA, Assistant Examiner US. Cl. X.R. 102-27 R

